Graphene electronic device and method of fabricating the same

ABSTRACT

Provided are a method of fabricating a graphene electronic device and the graphene electronic device fabricated thereby. The method may include forming a first electrode and a second electrode spaced apart from each other, on a substrate, forming supporting patterns on the first electrode and the second electrode, coating the supporting patterns with graphene-oxide-containing solution to form composite patterns, and separating the supporting patterns from the composite patterns.

CROSS-REFERENCE TO RELATED APPLICATIONS

This U.S. non-provisional patent application claims priority under 35U.S.C. §119 to Korean Patent Application Nos. 10-2012-0054437 and10-2012-0086796, filed on May 22, 2012 and Aug. 8, 2012, respectively,in the Korean Intellectual Property Office, the entire contents of whichare hereby incorporated by reference.

BACKGROUND OF THE INVENTION

Example embodiments of the inventive concept relate to an electronicdevice and a method of fabricating the same, and in particular, to agraphene electronic device and a method of fabricating the same.

Graphene a substance composed of pure carbon, with atomstwo-dimensionally arranged in a regular hexagonal pattern similar tographite. Graphene can be obtained from graphite crystals, for example,using an adhesive tape (e.g., a scotch tape). Graphene exhibitsexcellent electric characteristics, such as high conductivity of1×10⁻⁶Ωcm and high electron mobility, as well as excellent materialcharacteristics, such as a large surface area of 2650 m²/g, that islarger than two times that of active carbon, a high elasticity modulusof 1 TPa, and high chemical stability. In addition, after seeing therecent report about graphene as an antibacterial material, graphene isin the spotlight. In this sense, there are many researches to usegraphene in fields of display, lithium-ion cell, capacitor electrode,Environmental Filter, and biotechnology.

SUMMARY

Example embodiments of the inventive concept provide a method capable ofeasily fabricating a graphene electronic device with a large areagraphene channel.

Other example embodiments of the inventive concept provide a grapheneelectronic device with a large area graphene channel.

According to example embodiments of the inventive concepts, a method offabricating a graphene electronic device may include forming a firstelectrode and a second electrode spaced apart from each other, on asubstrate, forming supporting patterns on the first electrode and thesecond electrode, coating the supporting patterns withgraphene-oxide-containing solution to form composite patterns, andseparating the supporting patterns from the composite patterns.

In example embodiments, the supporting patterns may be formed to connectthe first electrode to the second electrode.

In example embodiments, the supporting patterns include polymer fibers.

In example embodiments, the forming of the supporting patterns mayinclude providing a mask on the first and second electrodes, andelectrospinning a polymer solution on the first and second electrodeswith the mask. The mask may be formed to expose end portions of thefirst and second electrodes and the substrate between the end portions.

In example embodiments, the supporting patterns may be formed spacedapart from the substrate to connect the end portions of the first andsecond electrodes to each other.

In example embodiments, the forming of the supporting patterns mayfurther include using ammonia solution or sodium hydroxide solution tomake the supporting patterns insoluble.

In example embodiments, the coating of the supporting patterns withgraphene-oxide-containing solution may be performed in such a way thatgraphene oxide in the graphene-oxide-containing solution may beself-assembled with the supporting patterns.

In example embodiments, the separating of the supporting patterns fromthe composite patterns may include thermally treating or chemicallydissolving an electronic device including the composite patterns.

In example embodiments, the chemical dissolving may be performed usingacidic solvent.

In example embodiments, the coating of the supporting patterns withgraphene-oxide-containing solution may include dipping the supportingpatterns into the graphene-oxide-containing solution to form grapheneoxide composite patterns, and reducing the graphene oxide compositepatterns to graphene composite patterns.

In example embodiments, the reducing of the graphene oxide compositepatterns to the graphene composite patterns may be performed using athermal, optical, or chemical method.

According to example embodiments of the inventive concepts, a grapheneelectronic device may include a substrate, a first electrode and asecond electrode provided on the substrate and spaced apart from eachother, and graphene channels connecting the first electrode with thesecond electrode. Each of the graphene channels may be separated fromthe substrate to have a cylindrical structure. In addition, each of thegraphene channels may include graphene or graphene oxide and have aninner diameter of about 1 nm to about 100 μm.

BRIEF DESCRIPTION OF THE DRAWINGS

Example embodiments will be more clearly understood from the followingbrief description taken in conjunction with the accompanying drawings.The accompanying drawings represent non-limiting, example embodiments asdescribed herein.

FIG. 1 is a flow chart illustrating a method of fabricating a grapheneelectronic device according to example embodiments of the inventiveconcept.

FIGS. 2A through 9C are provided to describe a graphene electronicdevice according to example embodiments of the inventive concept and amethod of fabricating the same.

FIG. 10 is a flow chart illustrating a method of fabricating a grapheneelectronic device according to other example embodiments of theinventive concept.

FIGS. 11A through 12C are provided to describe a graphene electronicdevice according to other example embodiments of the inventive conceptand a method of fabricating the same.

It should be noted that these figures are intended to illustrate thegeneral characteristics of methods, structure and/or materials utilizedin certain example embodiments and to supplement the written descriptionprovided below. These drawings are not, however, to scale and may notprecisely reflect the precise structural or performance characteristicsof any given embodiment, and should not be interpreted as defining orlimiting the range of values or properties encompassed by exampleembodiments. For example, the relative thicknesses and positioning ofmolecules, layers, regions and/or structural elements may be reduced orexaggerated for clarity. The use of similar or identical referencenumbers in the various drawings is intended to indicate the presence ofa similar or identical element or feature.

DETAILED DESCRIPTION

Example embodiments of the inventive concepts will now be described morefully with reference to the accompanying drawings, in which exampleembodiments are shown. Example embodiments of the inventive conceptsmay, however, be embodied in many different forms and should not beconstrued as being limited to the embodiments set forth herein; rather,these embodiments are provided so that this disclosure will be thoroughand complete, and will fully convey the concept of example embodimentsto those of ordinary skill in the art. In the drawings, the thicknessesof layers and regions are exaggerated for clarity. Like referencenumerals in the drawings denote like elements, and thus theirdescription will be omitted.

It will be understood that when an element is referred to as being“connected” or “coupled” to another element, it can be directlyconnected or coupled to the other element or intervening elements may bepresent. In contrast, when an element is referred to as being “directlyconnected” or “directly coupled” to another element, there are nointervening elements present. Like numbers indicate like elementsthroughout. As used herein the term “and/or” includes any and allcombinations of one or more of the associated listed items. Other wordsused to describe the relationship between elements or layers should beinterpreted in a like fashion (e.g., “between” versus “directlybetween,” “adjacent” versus “directly adjacent,” “on” versus “directlyon”).

It will be understood that, although the terms “first”, “second”, etc.may be used herein to describe various elements, components, regions,layers and/or sections, these elements, components, regions, layersand/or sections should not be limited by these terms. These terms areonly used to distinguish one element, component, region, layer orsection from another element, component, region, layer or section. Thus,a first element, component, region, layer or section discussed belowcould be termed a second element, component, region, layer or sectionwithout departing from the teachings of example embodiments.

Spatially relative terms, such as “beneath,” “below,” “lower,” “above,”“upper” and the like, may be used herein for ease of description todescribe one element or feature's relationship to another element(s) orfeature(s) as illustrated in the figures. It will be understood that thespatially relative terms are intended to encompass differentorientations of the device in use or operation in addition to theorientation depicted in the figures. For example, if the device in thefigures is turned over, elements described as “below” or “beneath” otherelements or features would then be oriented “above” the other elementsor features. Thus, the exemplary term “below” can encompass both anorientation of above and below. The device may be otherwise oriented(rotated 90 degrees or at other orientations) and the spatially relativedescriptors used herein interpreted accordingly.

The terminology used herein is for the purpose of describing particularembodiments only and is not intended to be limiting of exampleembodiments. As used herein, the singular forms “a,” “an” and “the” areintended to include the plural forms as well, unless the context clearlyindicates otherwise. It will be further understood that the terms“comprises”, “comprising”, “includes” and/or “including,” if usedherein, specify the presence of stated features, integers, steps,operations, elements and/or components, but do not preclude the presenceor addition of one or more other features, integers, steps, operations,elements, components and/or groups thereof.

Example embodiments of the inventive concepts are described herein withreference to cross-sectional illustrations that are schematicillustrations of idealized embodiments (and intermediate structures) ofexample embodiments. As such, variations from the shapes of theillustrations as a result, for example, of manufacturing techniquesand/or tolerances, are to be expected. Thus, example embodiments of theinventive concepts should not be construed as limited to the particularshapes of regions illustrated herein but are to include deviations inshapes that result, for example, from manufacturing. For example, animplanted region illustrated as a rectangle may have rounded or curvedfeatures and/or a gradient of implant concentration at its edges ratherthan a binary change from implanted to non-implanted region. Likewise, aburied region formed by implantation may result in some implantation inthe region between the buried region and the surface through which theimplantation takes place. Thus, the regions illustrated in the figuresare schematic in nature and their shapes are not intended to illustratethe actual shape of a region of a device and are not intended to limitthe scope of example embodiments.

Unless otherwise defined, all terms (including technical and scientificterms) used herein have the same meaning as commonly understood by oneof ordinary skill in the art to which example embodiments of theinventive concepts belong. It will be further understood that terms,such as those defined in commonly-used dictionaries, should beinterpreted as having a meaning that is consistent with their meaning inthe context of the relevant art and will not be interpreted in anidealized or overly formal sense unless expressly so defined herein.

FIGS. 1 through 9C are provided to describe a method of fabricating agraphene electronic device according to example embodiments of theinventive concept. FIGS. 2A, 3A, 4A, 6A, and 9A are plan viewsillustrating the graphene electronic device according to exampleembodiments of the inventive concept, and FIGS. 2B, 3B, 4B, 6B, and 9Bare sectional views taken along line A-A′ of FIG. 2A, line B-B′ of FIG.3A, line C-C′ of FIG. 4A, line D-D′ of FIG. 6A, and line E-E of FIG. 9A,respectively.

Referring to FIGS. 1, 2A, and 2B, a substrate 10 is provided (in S10).For example, the substrate 10 may be a silicon wafer. Electrodes 20 maybe provided on the substrate 10. The electrodes 20 may include a firstelectrode 21 and a second electrode 22. The first electrode 21 and thesecond electrode 22 may serve as a source electrode and a drainelectrode, respectively. The first electrode 21 and the second electrode22 may be formed spaced apart from each other, on the substrate 10. Thefirst electrode 21 may include a first electrode body 21 a and a firstelectrode extension 21 b extending from the first electrode body 21 a.The first electrode extension 21 b may include a first extension 1EXextending from the first electrode body 21 a along an x-direction and asecond extension 2EX extending from the first extension 1EX along ay-direction, where the x- and the y-directions may cross each other. Thesecond electrode 22 may include a second electrode body 22 a and asecond electrode extension 22 b extending from the second electrode body22 a. The second electrode extension 22 b may include a third extension3EX extending from the second electrode body 22 a along an oppositedirection of the x-direction and a fourth extension 4EX extending fromthe third extension 3EX along an opposite direction of the y-direction.The electrodes 20 may have a uniform thickness, when measured along az-direction that is perpendicular to a top surface of the substrate 10.In example embodiments, as exemplarily shown in FIGS. 2C through 2E, thefirst electrode 21 and the second electrode 22 may be formed to havevarious structures that are modified from that shown in FIG. 2A.

The electrodes 20 may be formed using an optical lithography process oran e-beam lithography process. The first electrode 21 and the secondelectrode 22 may be formed a conductive material. For example, theconductive material may include at least one of gold, silver, aluminum,copper, palladium, platinum, silicon, polysilicon, conductive polymer,carbon nanotube, or graphene.

Referring to FIGS. 3A and 3B, a mask 30 may be provided on theelectrodes 20. The mask 30 may be in contact with top surfaces of theelectrodes 20. The mask 30 may be formed to expose the second extension2EX of the first electrode 21, the fourth extension 4EX of the secondelectrode 22, and the substrate 10 between the extensions 2EX and 4EX.The mask 30 may include at least one of, for example, glass, quartz,acrylic, printed circuit board (PCB) substrate, or OHP film.

Referring to FIGS. 1, 4A, and 4B, supporting patterns 40 may be formedon the electrodes 20 (in S20). The supporting patterns 40 may bepartially overlapped with the electrodes 20 and thereby connect thefirst electrode 21 to the second electrode 22. For example, thesupporting patterns 40 may be formed vertically spaced apart from thesubstrate 10 to connect the second extension 2EX of the first electrode21 to the fourth extension 4EX of the second electrode 22. In exampleembodiments, the supporting patterns 40 may include a polymer fiber. Inexample embodiments, the formation of the supporting patterns 40 mayinclude a step of electrospinning polymer solution on the substrate 10.

The polymer solution may be provided in the form of polymer-containingsolvent. The polymer provided in the solvent may include at least one ofpolyamide-6, polyamide-6,6, polyurehthanes, polybenzimidazole,polyacrylonitrile, polyaniline (PANI), polyvinylcarbazole,polyacrylamide (PAAm), polyimide, poly-metaphenyleneisophtalamides,poly-L-lysine, betaamyloid, collagen, fibrin, chitosan, or gelatin. Thesolvent may include at least one of water, ethanol, methanol, acetone,phosphate buffered saline (PBS) buffer, acetic acid (C₂H₄O₂), formicacid (CH₂O₂), hexafluoro-2-propanol ((CF₃)₂CHOH), trifluoroaceticacid(C₂HF₃O₂), dichloromethane (CH₂Cl₂), acetonitrile (C₂H₃N), benzene(C₆H₆), 1-butanol (C₄H₁₀O), 2-butanol (C₄H₁₀O), 2-butanone (C₄H₈O),t-butyl alcohol (C₄H₁₀O), carbon tetrachloride (CCl₄), chlorobenzene(C₆H₅Cl), chloroform (CHCl₃), cyclohexane (C₆H₁₂), 1,2-dichloroethane(C₂H₄Cl₂), chlorobenzene, dichloromethane (CH₂Cl₂), ethyl ether(C₄H₁₀O), diethylene glycol (C₄H₁₀O₃), diglyme (diethylene glycol,dimethyl ether) (C₆H₁₄O₃), 1,2-dimethoxy-ethane (glyme, DME) (C₄H₁₀O₂),dimethylether (C₂H₆O), dimethyl-formamide (DMF) (C₃H₇NO), dimethylsulfoxide (DMSO) (C₂H₆OS), dioxane (C₄H₈O2), ethyl acetate (C₄H₈O₂),ethylene glycol (C₂H₆O₂), glycerin (C₃H₈O₃), heptane (C₇H₁₆),hexamethylphosphoramide (HMPA) (C₆H₁₈N₃OP),hexamethylphosphoroustriamide (HMPT) (C₆H₁₈N₃P), hexane (C₆H₁₄), methylt-butyl ether (MTBE) (C₅H₁₂O), methylene chloride (CH₂Cl₂),N-methyl-2-pyrrolidinone (NMP) (CH₅H₉NO), nitromethane (CH₃NO₂), pentane(C₅H₁₂), Petroleum ether (ligroine), 1-propanol (C₃H₈O), 2-propanol(C₃H₈O), pyridine (C₅H₅N), tetrahydrofuran (THF) (C₄H₈O), toluene(C₇H₈), triethyl amine (C₆H₁₅N), o-xylene (C₈H₁₀), m-xylene (C₈H₁₀), orp-xylene (C₈H₁₀). In example embodiments, the polymer solution may beprovided to have a concentration of about 0.1 to 50 wt % (weightpercent).

The supporting patterns 40 may be formed using an electrospinningapparatus 100 shown in FIG. 5. For example, the electrospinningapparatus 100 may include a current collector 55. The current collector55 may include a first supporting part 54 and a second supporting part53 on the first supporting part 54. The current collector 55 may includean insulating material. In example embodiments, the insulating materialmay include at least one of glass, quartz, acrylic, OHP film,polyethylene terephthalate (PET), polyethylene naphthalate (PEN), PES,PEEK, polyimide (PI), polynorbonene, polyarylate, polycarbonate (PC),PAR, polydimethylsiloxane (PDMS), or non-woven fabrics. The substrate 10with the mask 30 (of FIGS. 3A and 3B) may be provided on the secondsupporting part 53. The mask 30 may expose the second extension 2EX ofthe first electrode 21, the fourth extension 4EX of the second electrode22, and the substrate 10 between the extensions 2EX and 4EX. The mask 30may prevent the supporting patterns 40 from being formed beyond thesecond extension 2EX of the first electrode 21 and the fourth extension4EX of the second electrode 22. A polymer solution 56 may be suppliedinto a cylinder 51 and be electrospun onto a portion of the substrate10, which is exposed by the mask 30, through a nozzle 52 of the cylinder51. The nozzle 52 may be configured to be a single mode. For example,the nozzle 52 may be configured to have a single hole. In otherembodiments, the nozzle 52 may be configured to be a multimode. Forexample, the nozzle 52 may be configured to have two or more holes. Inexample embodiments, the nozzle 52 may be provided to be a dual mode orhave two holes including a first hole and a ring-shaped second holesurrounding the first hole. A specific voltage may be applied betweenthe nozzle 52 and the electrodes 20. In example embodiments, a diameterof the supporting pattern may be controlled by adjusting the voltageapplied between the nozzle 52 and the electrodes 20. In exampleembodiments, the supporting patterns may have a diameter ranging fromabout 1 nm to 100 μm. The supporting patterns 40 may be formed to havevarious shapes, such as a single line shape or mesh shape, depending ona shape of the electrodes 20 provided on the substrate 10. For example,the supporting patterns 40 may include a plurality of supportingpatterns that connect the second extension 2EX of the first electrode tothe fourth extension 4EX of the second electrode, as shown in FIGS. 4Aand 4B and are provided spaced apart from the substrate 10. The mask 30may be removed after the formation of the supporting patterns 40, asshown in FIGS. 4A and 4B. The supporting patterns 40 may be neutralizedusing ammonia solution or sodium hydroxide solution (NaOH), therebyhaving insolubility.

Referring to FIGS. 1 and 6A through 6C, graphene oxide compositepatterns 60 may be formed (in S30). Here, FIG. 6C is a sectional view ofa portion P of FIG. 6B. The graphene oxide composite patterns 60 may beformed on surfaces of the electrodes 20 to connect the first electrode21 to the second electrode 22. For example, the graphene oxide compositepatterns 60 may connect the second extension 2EX of the first electrode21 to the fourth extension 4EX of the second electrode 22 and be spacedapart from the substrate 10. Each of the graphene oxide compositepatterns 60 may consist of the supporting pattern 40 and a grapheneoxide structure 63 surrounding the supporting pattern 40.

The formation of the graphene oxide composite patterns 60 may includedipping the substrate 10 provided with the supporting patterns 40 intographene-oxide-containing solution (in the step of S20). For example, asshown in FIG. 7, the substrate 10 provided with the supporting patterns40 may be dipped into graphene-oxide-containing solution 61. Thesupporting patterns 40 may have insolubility, as the result of theafore-described neutralization treatment, and thus, they may not bedissolved by the graphene-oxide-containing solution. FIG. 8 is aschematic diagram illustrating a portion Q of FIG. 7.

The graphene-oxide-containing solution 61 may be prepared by dispersinga graphene oxide 62 into solvent. In example embodiments, the solventmay include at least one of water, acetic acid (C₂H₄O₂), acetone(C₃H₆O), acetonitrile (C₂H₃N), benzene (C₆H₆), 1-butanol (C₄H₁₀O),2-butanol (C₄H₁₀O), 2-butanone (C₄H₈O), t-butyl alcohol (C₄H₁₀O), carbontetrachloride (CCl₄), chlorobenzene (C₆H₅Cl), chloroform (CHCl₃),cyclohexane (C₆H₁₂), 1,2-dichloroethane (C₂H₄Cl₂), chlorobenzene,dichloromethane (CH₂Cl₂), ethyl ether (C₄H₁₀O), diethylene glycol(C₄H₁₀O₃), diglyme (diethylene glycol, dimethyl ether) (C₆H₁₄O₃),1,2-dimethoxy-ethane (glyme,DME) (C₄H₁₀O₂), dimethylether (C₂H₆O),dimethyl-formamide (DMF) (C₃H₇NO), dimethyl sulfoxide (DMSO) (C₂H₆OS),dioxane (C₄H₈O₂), ethanol (C₂H₆O), ethyl acetate (C₄H₈O₂), ethyleneglycol (C₂H₆O₂), glycerin (C₃H₈O₃), heptane (C₇H₁₆),hexamethylphosphoramide (HMPA) (C₆H₁₈N₃OP),hexamethylphosphoroustriamide (HMPT) (C₆H₁₈N₃P), hexane (C₆H₁₄),methanol (CH₄O), methyl t-butyl ether (MTBE) (C₅H₁₂O), methylenechloride (CH₂Cl₂), N-methyl-2-pyrrolidinone (NMP) (CH₅H₉NO),nitromethane (CH₃NO₂), pentane (C₅H₁₂), petroleum ether (ligroine),1-propanol (C₃H₈O), 2-propanol (C₃H₈O), pyridine (C₅H₅N),tetrahydrofuran (THF) (C₄H₈O), Toluene (C₇H₈), triethyl amine (C₆H₁₅N),o-xylene (C₈H₁₀), m-xylene (C₈H₁₀), or p-xylene (C₈H₁₀).

Hydrogen chloride solution may be added into thegraphene-oxide-containing solution 61 to obtain a hydrogen ionconcentration (pH) of about 5 or less. The supporting patterns 40 mayhave a positively charged surface, and the graphene oxide 62 in thegraphene-oxide-containing solution 61 may be negatively charged. Thenegatively charged graphene oxide 62 may be self-assembled on thepositively charged surface of the supporting patterns 40, therebyforming the graphene oxide structures 63.

Referring to FIGS. 1 and 9A through 9C, the supporting patterns 40 maybe separated from the graphene oxide composite patterns 60 (in S40).Here, FIG. 9C is a sectional view of a portion R of FIG. 9B. As theresult of the removal of the supporting patterns 40, gap regions 70 thatare empty spaces may be formed in the graphene oxide structures 63. Thesupporting patterns 40 may be separated from the graphene oxidecomposite patterns 60 by a thermal treatment or a chemical dissolution.For example, the electronic device with the graphene oxide compositepatterns 60 may be thermally treated in a temperature ranging from about25° C. to about 3000° C. (preferably, from about 100° C. to about 3000°C.) for about 1 minute to 24 hours. The chemical dissolution may beperformed using acidic solvent, which may include at least one of aceticacid (C₂H₄O₂), formic acid (HCOOH), citric acid (C₆H₈O₇), hydrochloricacid (HCl), sulfuric acid (H₂SO₄), nitric acid (HNO₃), perchloric acid(HClO₄), fluoric acid (HF), phosphoric acid (H₃PO₄), chromic acid(HCrO4), propionic acid (CH3CH2COOH), oxalic acid, glycol acid, tartaricacid (C₄H_(S)O₆) acetone, or toluene.

The graphene electronic device with the graphene oxide structures 63will be described in more detail with reference to FIGS. 9A through 9C.The graphene oxide structures 63 may serve as channels connecting thefirst electrode 21 with the second electrode 22. In example embodiments,each of the graphene oxide structures 63 may be provided to have acylindrical structure. For example, each of the graphene oxidestructures 63 may include an outer surface and an inner surface definingthe gap region 70. The gap region 70 may have an internal diameterranging from about 1 nm to about 100 μm.

FIGS. 10 through 12C are provided to describe a graphene electronicdevice according to other example embodiments of the inventive conceptand a method of fabricating the same. For the sake of brevity, theelements and features of this example that are similar to thosepreviously shown and described will not be described in much furtherdetail. FIGS. 11A and 12A are plan views illustrating the grapheneelectronic device according to other example embodiments of theinventive concept, and FIGS. 11B and 12B are sectional views taken alongline F-F′ of FIG. 11A and line G-G′ of FIG. 12A. FIG. 11C is a sectionalview of a portion S of FIG. 11B, and FIG. 12C is a sectional view of aportion T of FIG. 12B.

Referring to FIGS. 10 and 11A through 11C, the graphene oxide compositepatterns 60 may be formed by performing the steps of S10, S20, and S30,which were described in the previous embodiments, in the substantiallysame manner, and graphene composite patterns 80 may be formed from thegraphene oxide composite patterns 60 (in S35). Each of the graphenecomposite patterns 80 may include the supporting pattern 40 and agraphene structure 85 surrounding the supporting pattern 40. Thegraphene composite patterns 80 may be formed by performing a reductionprocess on the graphene oxide composite patterns 60 shown in FIGS. 6Aand 6B. The reduction process may be performed using one of thermal,optical, and chemical methods. For example, the thermal reduction may beperformed at a temperature of about 40° C. to about 2000° C. The opticalreduction may be performed using light having wavelength of about 200 nmto about 1500 nm. The chemical reduction may be performed using at leastone of hydriodic acid with acetic acid (HI—AcOH), hydrazine (N₂H₄),dimethyl hydrazine (C₂H₈N₂), sodium borohydride (NaBH₄), sodiumhydroxide (NaOH), ascorbic acid, glucose, hydrogen sulfide (H₂S),hydroquinone (C₆H₄(OH)₂), or sulfuric acid (H₂SO₄).

Referring to FIGS. 10 and 12A through 12C, the supporting patterns 40may be separated from the graphene composite patterns 80 (in S40). Thesupporting patterns 40 may be separated from the graphene compositepatterns 80 by a thermal treatment or a chemical dissolution. Thethermal treatment or the chemical dissolution may be performed in thesame manner as that in the step S40 of the previous embodimentsdescribed with reference to FIG. 1.

The graphene electronic device with the graphene structures 85 will bedescribed in more detail with reference to FIGS. FIGS. 12A through 12C.The graphene structures 85 may serve as channels connecting the firstelectrode 21 with the second electrode 22. For example, each of thegraphene structures 85 may be provided to have a cylindrical structure.In example embodiments, each of the graphene structures 85 may includean outer surface and an inner surface defining the gap region 70. Thegap region 70 may have an internal diameter ranging from about 1 nm toabout 100 μm.

Hereinafter, experimental examples according to example embodiments ofthe inventive concept will be described to provide better understandingof example embodiments of the inventive concepts, but exampleembodiments of the inventive concepts may not be limited thereto.

EXPERIMENTAL EXAMPLE 1 Using Chitosan Polymer

Using the method described in the step S10, a substrate was provided.The substrate was a silicon wafer. The substrate was cleaned by piranhasolution containing hydrogen peroxide and sulfuric acid and cleanedthree times by distilled water. A first electrode and a second electrodewere formed on the cleaned substrate using an optical or e-beamlithography technique. The first electrode and the second electrode wereformed spaced apart from each other, as shown in FIG. 2A.

Using the method described in the step S20, supporting patterns wereformed on the substrate. Chitosan solution was prepared by addingchitosan powder, which was purchased from Sigma-aldrich, intrifluoroacetic acid solution and then mixing them using an agitator at50° C. for six hours.

The substrate with the electrodes was provided on the current collectorof the electrospinning apparatus described with reference to FIG. 5. Amask was provided on the electrodes to expose end portions of the firstand second electrodes and the substrate between the end portions. Themask was a PCB substrate.

The prepared chitosan solution was supplied into the cylinder describedwith reference to FIG. 5, and thereafter, an electrospinning wasperformed on the current collector under an applied voltage of 15 kV anda solution injection speed of 1-5 ml/h. During the electrospinning, adistance between the cylinder and the current collector was 10 cm.Depending on the process conditions, such as a concentration of thechitosan solution and the applied voltage, chitosan fibers, i.e.,supporting patterns, were formed to have a diameter ranging from severaltens of nanometers to several micrometers. The electronic device withthe supporting patterns was dipped into ammonia solution for four hoursto neutralize it, and then, was cleaned three times by distilled water.As a result, the supporting patterns were prepared to have insolubility.

Using the method described in the step S30, graphene oxide compositepatterns were formed on the substrate. Firstly,graphene-oxide-containing solution was prepared. Graphene oxide wasformed by a modified Hummers and Offenman method using graphite powder(Bay carbon, SP-1 graphite). The graphene oxide powder was added indistilled water with a ratio of 0.01-1 mg/ml, and then, the solution wasdispersed, for four hours, by an ultrasonic method. Thereafter, thegraphene oxide solution was adjusted to have a hydrogen ionconcentration (pH) of about 4.3, and then, the electronic deviceprovided with the supporting patterns was dipped in the graphene oxidesolution for five hours or more. The graphene oxide composite patternswere formed as the result of a self-assembly between an amide groupformed on surfaces of the supporting patterns and an epoxy group, ahydroxyl group, and a carboxyl group of the graphene oxide. Theelectronic device including the graphene oxide composite patterns wascleaned three times with distilled water and was dried with nitrogengas.

Using the method described in the step S35, the graphene oxide compositepatterns were reduced to form graphene composite patterns on thesubstrate. The reduction was performed using hydriodic acid with aceticacid (HI—AcOH) solution. In more detail, the electronic device includinggraphene oxide composite patterns was dipped into and reacted with mixedsolution containing 2 ml of hydriodic acid and 5 ml of acetic acid, at atemperature of 40° C. for 24 hours. As a result, the electronic deviceincluding the reduced graphene composite patterns was prepared.

Using the method described in the step S40, the supporting patterns wereseparated from the reduced graphene composite patterns. In more detail,the electronic device including the graphene composite patterns wasthermally treated at a temperature of about 100 to 200° C. for 24 hoursor dipped into acidic solvent for 30 minutes, thereby removing thechitosan fibers supporting graphene. As a result, the grapheneelectronic device was completed.

EXPERIMENTAL EXAMPLE 2 Using Nylon Polymer

Using the method described in the step S10, a substrate with electrodeswas provided.

Using the method described in the step S20, supporting patterns wereformed on the substrate. Nylon solution was prepared by adding nylon-6powder, which was purchased from Sigma-aldrich, in formic acid solutionand then mixing them using an agitator at 50° C. for six hours.

The substrate with the electrodes was provided on the current collectorof the electrospinning apparatus described with reference to FIG. 5. Amask was provided on the electrodes to expose end portions of the firstand second electrodes and the substrate between the end portions.

The prepared nylon solution was supplied into the cylinder describedwith reference to FIG. 5, and thereafter, an electrospinning wasperformed on the current collector under an applied voltage of 15 kV anda solution injection speed of 0.5-5 ml/h. During the electrospinning, adistance between the cylinder and the current collector was 10 cm.Depending on the process conditions, such as a concentration of thenylon solution and the applied voltage, nylon fibers, i.e., supportingpatterns, were formed to have a diameter ranging from several tens ofnanometers to several micrometers. The electronic device including thesupporting patterns was dried in a hood.

Using the method described in the step S30, graphene oxide compositepatterns were formed in the same manner as that of the experimentalexample 1. Thereafter, the graphene oxide solution was adjusted to havea hydrogen ion concentration (pH) of about 4.3, and then, the electronicdevice provided with the supporting patterns was dipped in the grapheneoxide solution for five hours or more. The graphene oxide compositepatterns were formed as the result of a self-assembly between an amidegroup formed on surfaces of the supporting patterns and an epoxy group,a hydroxyl group, and a carboxyl group of the graphene oxide. Theelectronic device including the graphene oxide composite patterns wascleaned three times with distilled water and was dried with nitrogengas.

Using the method described in the step S35, similar to the experimentalexample 1, the electronic device including the graphene oxide compositepatterns was reduced to form the graphene composite patterns.

Using the method described in the step S40, similar to the experimentalexample 1, the supporting patterns of nylon were separated from thereduced graphene composite patterns. As a result, the grapheneelectronic device was completed.

According to example embodiments of the inventive concept, it ispossible to form a graphene electronic device with a cylindricalgraphene channel. In addition, a diameter of the graphene channel can beeasily controlled by changing a process condition of the electrospinningprocess for forming the supporting patterns. Further, according toexample embodiments of the inventive concept, it is possible to form thegraphene electronic device on not only a rigid substrate (e.g., ofsilicon, glass, single crystalline wafer) but also a flexible substrate(e.g., of PDMS, PET polyimide).

According to example embodiments of the inventive concept, it ispossible to fabricate a graphene electronic device with a large areagraphene channel with ease.

While example embodiments of the inventive concepts have beenparticularly shown and described, it will be understood by one ofordinary skill in the art that variations in form and detail may be madetherein without departing from the spirit and scope of the attachedclaims.

What is claimed is:
 1. A method of fabricating a graphene electronicdevice, comprising: forming a first electrode and a second electrodespaced apart from each other, on a substrate; forming supportingpatterns on the first electrode and the second electrode; coating thesupporting patterns with graphene-oxide-containing solution to formcomposite patterns; and separating the supporting patterns from thecomposite patterns.
 2. The method of claim 1, wherein the supportingpatterns are formed to connect the first electrode to the secondelectrode.
 3. The method of claim 1, wherein the supporting patternscomprise polymer fibers.
 4. The method of claim 1, wherein the formingof the supporting patterns comprises: providing a mask on the first andsecond electrodes; and electrospinning a polymer solution on the firstand second electrodes with the mask, wherein the mask is formed toexpose end portions of the first and second electrodes and the substratebetween the end portions.
 5. The method of claim 4, wherein thesupporting patterns are formed spaced apart from the substrate toconnect the end portions of the first and second electrodes to eachother.
 6. The method of claim 4, wherein the forming of the supportingpatterns further comprises using ammonia solution or sodium hydroxidesolution to make the supporting patterns insoluble.
 7. The method ofclaim 1, wherein the coating of the supporting patterns withgraphene-oxide-containing solution is performed in such a way thatgraphene oxide in the graphene-oxide-containing solution isself-assembled with the supporting patterns.
 8. The method of claim 1,wherein the separating of the supporting patterns from the compositepatterns comprises thermally treating or chemically dissolving anelectronic device including the composite patterns.
 9. The method ofclaim 8, wherein the chemical dissolving is performed using acidicsolvent.
 10. The method of claim 1, wherein the coating of thesupporting patterns with graphene-oxide-containing solution comprises:dipping the supporting patterns into the graphene-oxide-containingsolution to form graphene oxide composite patterns; and reducing thegraphene oxide composite patterns to graphene composite patterns. 11.The method of claim 10, wherein the reducing of the graphene oxidecomposite patterns to the graphene composite patterns is performed usinga thermal, optical, or chemical method.
 12. A graphene electronicdevice, comprising: a substrate; a first electrode and a secondelectrode provided on the substrate and spaced apart from each other;and graphene channels connecting the first electrode with the secondelectrode, wherein each of the graphene channels is separated from thesubstrate to have a cylindrical structure.
 13. The device of claim 12,wherein each of the graphene channels comprises graphene or grapheneoxide.
 14. The device of claim 12, wherein each of the graphene channelshas an inner diameter of 1 nm to 100 μm.